If you want to know what to wear to your first Carnival ball, ask the woman who knows the inside terms “valet shoes” and “jewelry dress” and who has at least one floor-length gown with a frayed hem from too much wear. She is a veteran of such affairs, and your best interpreter of costume de rigueur.

Basically, here are the fashion dictates for women:

1. Floor-length gowns, never pants (don’t even breathe the word palazzo). Do not wear white or cream; only members of the court wear white.

2. Evening jewelry, not your daytime baubles. This is the time for pearls and stones and pieces that sparkle. Faux is fine.

4. Elegant shawls or evening coats. Check the forecast. This is New Orleans. You never know if you will need a light or heavy wrap.

5. An evening bag that holds only the essentials. Those giant totes are for work; an evening bag is for play. You are going to play, aren’t you? Make sure your invitation is inside; you will need it to enter the ball.

6. White kid opera-length gloves (or a length suited to the sleeve of the ball gown) if you are sitting on the front row.

Yes, there is ball protocol, but there is also room for panache.

“Every woman should love wearing floor-length gowns. The night is not just for the mock royalty, but for all of us to participate in the fun and magic of dressing up for a ball,” says Virginia Saussy, a marketing consultant who gives frequent lectures on Carnival at local universities and conventions, and has a résumé of ball attendance from Apollo to Zulu.

“Follow protocol, but be as creative as you want to be that night,” says Naydja Bynum, who has accumulated four decades of dressing for multiple and varied Carnival balls. “The fantasy of the occasion is part of the fun.”

But even fantasy has its limits.

“They check the length (of the gown) when you present your invitation, and it doesn’t matter who you are. If your dress isn’t floor length — to the floor, not tea length or shorter in the front than the back — you aren’t entering,” says Kathleen White, whose daughter, Jane Yvonne White, reigned as queen of Carnival in 2011.

Basic black is every woman’s go-to look, but Carnival is also a time to celebrate wearing color.

“For those who have a reserved seat on the front row, there is an unspoken rule that you never wear black. Because the ball is televised and played live, color stands out and looks prettier,” says White, referring to the Rex ball of which her daughter, Jane Yvonne, was queen in 2011.

But for women attending any ball, Carnival is still an opportunity to be festive rather than limited to wearing everywoman’s basic black. There is one drawback, however, to wearing a colorful ball gown: the more striking the dress, the less mileage it gets.

For Tina Freeman, a former queen of Carnival, her choice for a show-stopping gown was all about contrast — black and white.

“I had to retire it often because people remembered it,” she says.

But there are many tricks veterans of Carnival balls employ to extend the life of a gown.

Freeman, through her dressmaker, often attaches a sense of history to some of her formal gowns. Some even lace up the back (another trick to a custom fit). The beauty of a gown that has a costume feel about it, says Freeman, is that “it never goes out of style.” One of her favorite gowns was inspired by a 1898 John Singer Sargent portrait of Mrs. Asher B. Wertheimer, on display in the New Orleans Museum of Art.

A separate piece

Women who attend several balls in a season often work with their dressmakers to create interchangeable pieces, producing different looks. Freeman has opted for a simple black dress and two different evening coats, which created three distinct looks. Saussy often turns to a long black silk skirt worn with two different tops and other transformative pieces.

“I had one skirt, two tops, three sashes in different colors and a long silk evening coat. I got 10 outfits out of it,” said Saussy, who made this timeless purchase at Ballin’s years ago.

“But be careful with separates. Make sure the combination creates the look of a ball gown,” says one fashion insider who admits to keeping a silent tally of fashion faux pas.

Ball gowns run the gamut from couture gowns with four-digit and up price tags to savvy bargains, the latter of which can earn a woman some bragging rights.

“I had a mint-green gown I had purchased at Hudson’s (a discount store) for $10. I got so many compliments on it. You add long white gloves to almost any dress, and it looks good,” says Saussy.

From head to toe

So what are these terms “valet shoes” and “jewelry dress”?

“Valet shoes are the risky shoes you don; they are the higher heels you wear when you have valet parking or someone is dropping you off at the door,” says Saussy.

But even Cinderella would tire of stiletto glass slippers at a Carnival ball, so the word from the experts is to bring a spare pair of comfortable shoes that can stave off aching feet should the night grow, ahem, a bit long.

“Keep in mind that you are dancing and walking around, and some of this is done on cement or other hard floors,” says Naydja Bynum. “There are also parking issues, and you may have a distance to walk before you even get to the ball. For backup only, you should put a pair of silver or gold fold-up ballerina slippers in your purse.”

Others suggest choosing only the tried-and-true evening shoes you have worn to other affairs and thoroughly broken in. If a mid- or lower-heeled shoe has served you well at formal occasions in the past, you have probably found your dancing shoes.

And about those “jewelry dresses” … Freeman says the simplest dress offers the greatest potential for accessorizing, and thus multiple looks. Bijoux can be real or faux. Evening light is just right for camouflaging fake stones and turning up the sparkle, or go up to the insured-by-Lloyd’s-of-London level.

Weather or not

Last but not least, consider the weather.

“We have schizophrenic winters here. It can be cold and rainy or hot and muggy,” says Bynum. “When someone asks me what I will be wearing, it always depends on the weather.”

While evening coats are always elegant, the quickest and most affordable option for a cover-up is a wrap. Bynum keeps a variety of weights and styles in her closet.

“You want the minimum cover you need to keep from freezing. If there is no coat check, you don’t want to be dragging a heavy coat around all night,” says Bynum (also the designer of many of the pieces she has worn), who knows that checking the forecast a few days ahead of the ball can often lessen one’s load.

So, if your first Carnival ball invitation has arrived in the mail, check your sources, those who have donned kid gloves before you.

“If you don’t have a friend to ask, check with a salesperson at a reputable store that carries gowns,” says White. Among the upscale boutiques and other stores that have catered to Carnival are Mimi’s, Saks Fifth Avenue and Town & Country. But once you know the rules, you can find a ball gown that suits you and your budget at most department stores and resale shops.

Even with something as age-old as Carnival, don’t rule out some high-tech help. A Google search can bring up ball gown rental sources, and your smartphone can provide some local links. But the mystique of Mardi Gras remains. Even Siri answered my first question with, “Hmmmm, let me think …”